When the heat turns up in an overcrowded bar, patrons waiting for service tend to get thirstier. In the coming decades, a similar scenario may play out in the United States. According to a new study, more than a third of U.S. counties may be at "extreme" or "high" risk of water shortages by 2050. This won’t be due to a dearth in bartenders, of course, but the result of a swelling population, along with the potential temperature increases and precipitation changes associated with climate change.

The first strike against water supplies comes from increases in population. Projections suggest fairly linear growth between now and mid-century, meaning the U.S. will have about 419.9 million people in 2050 (up from its current population of 313,000,000). All of those additional Americana will have to drink, and eat food grown with water, and turn on lights powered by water-guzzling power plants.

Then there's climate change. Temperature is expected to increase somewhere between 1.5 and 3° Celsius, and the warming air will be able to hold more water. The resulting changes in precipitation aren't uniform by any means. Models suggest that Texas and the Gulf states will lose more than one inch per year, while the northeastern U.S. could get between two and four extra inches per year.

Notably, the study’s results are not meant to be taken as strict prognoses. "This is not intended as a prediction that water shortages will occur, but rather where they are more likely to occur, and where there might be greater pressure on public officials and water users to better characterize, and creatively manage demand and supply," said the study's lead author Sujoy Roy of Tetra Tech Research and Development, in a press release.

The end result of all this -- hotter temperatures, changed precipitation, more people withdrawing more water -- is that 412 of 3,141 counties (13 percent) in the lower 48 might be at "extreme" risk of water shortages in 2050. Another 608 counties will be at high risk, while 1,192 and 929 will be at moderate and low risk, respectively. Without climate change? Just 29 counties (less than 1 percent) would be at extreme risk, 271 at high risk, and more than 2,000 would be at low risk. It's enough to make you thirsty for real action on this whole climate change thing. I'll cheers to that.

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Dave Levitan is a freelance journalist based in Philadelphia. He has written for Discover, Scientific American, Grist, Yale e360, and many others. Find more of his writing at his website and follow him on Twitter @davelevitan.

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